Transmissible spongiform encephalopathies (TSE) are a group of rare neurodegenerative diseases which include Creutzfeldt-Jakob disease (CJD) in humans, scrapie in sheep, bovine spongiform encephalopathy (BSE) and chronic wasting disease (CWD) in mule deer and elk. TSE infectivity can cross species barriers. The fact that BSE has infected humans in Great Britain and concerns that CWD may act similarly in the US underscores the importance of understanding TSE pathogenesis and developing effective anti-TSE therapeutics. The precise nature of the infectious agent of the TSE diseases is unknown. Susceptibility to infection can be influenced by amino acid homology between a normal host protein (PrP-sen) and the abnormal proteinase K-resistant form of this protein, PrP-res. Formation of PrP-res is closely associated with infectivity and PrP-res has been hypothesized to be the infectious agent in the TSE diseases. However, PrP-res can be deposited in the brain as either diffuse, amyloid negative deposits or as dense, amyloid positive deposits. Amyloid forms of TSE appear to be less transmissible than non-amyloid forms, suggesting that there is a fundamental difference in how they trigger disease. Furthermore, it is unclear whether or not TSE diseases where PrP-res is deposited primarily as amyloid follow the same pathogenic processes as TSE diseases where PrP-res is deposited as non-amyloid forms. We are interested in understanding the molecular mechanisms underlying PrP amyloid formation and have begun to approach this issue using both in vitro and in vivo model systems. This project focuses on: 1) understanding the pathways of PrP amyloid formation and, 2) studying how mutations in PrP influence PrP-res amyloid formation in familial forms of TSE disease. In 2009, we used PrP peptides in a cell-free system of fibrillization to examine how different regions of the PrP molecule may influence PrP amyloid formation. We have also infected mice that express human PrP-sen without the GPI anchor with different types of human TSE. Our expectation is that, if these mice develop PrP amyloid, we can utilize them as an in vivo model system for human amyloid disease. Hereditary forms of TSE disease are associated with mutations within the PrP gene. One of these mutations is the insertion of extra copies of an eight amino acid motif (octapeptide repeat) into PrP. We have used an in vitro fibrillization model of this hereditary mutation to study how the repeat region influences the formation of both PrP-res and PrP amyloid. Last year, we demonstrated that environmental conditions could change the mechanism of fibril formation which in turn altered the ultrastructural properties of the amyloid. In 2009, we have gathered data suggesting that the octapeptide repeat region can significantly influence the final structure of both PrP-res and PrP amyloid. The structural influence of the octapeptide repeat region appears to be strain specific and thus may help to explain the different pathologies associated with different types of TSE infectivity.